Editor’s Exclusive: Speed-Testing Mathews Chills and Rock Mods

After a side trip to Alaska to hunt black bears, I finally got a chance to do some test shooting of the new Mathews Chill-X. I also tested the new Rock Mods, which can be retrofitted for the two previous Chill models, the Chill and the Chill-R.

The purpose of the Rock Mods is to give the entire Chill line a draw stop with a solid back wall. The first two versions of the Chill did not have a draw stop and had a softer wall at full draw. Some archers prefer the feel of a soft wall, but most of today’s bowhunters are opting for a solid wall.

Another feature of the Rock Mods is they are available in either 75 percent or 85 percent let-off. Again, this is a matter of feel for most archers—but there is an impact on performance as well. I wanted to know just how much impact, so I broke out my chronograph.

First, the parameters. I set all three bows—the Chill, Chill-R, and Chill-X—at precisely 70 pounds and all had 30-inch draw modules. All three bows had a string loop and a peep sight on the string, and all sported a Mathews-specific QAD Ultra Rest. I shot two arrow weights: an IBO arrow weighing 350 grains and, for some real-life bowhunting results, one of my 446-grain hunting arrows.

Once set up, I shot both arrows from the Chill and the Chill-R with their original modules (both 80 percent let-off) and the arrow speeds in feet-per-second are listed in the table below. Then I installed the 75 percent Rock Mods in each bow and shot the same two arrows. Finally, I installed the 85 percent Rock Mods in each of the three bows (results are also listed in the table below).

Here are some takeaways:

There was a modest gain in arrow speed, ranging from 2 to 4 fps, when going from the original 80 percent let-off modules on the Chill and Chill-R, to the new 75 percent Rock Mod. But again, this is mostly about feel. You’re essentially installing a solid back wall on your bow.

Switching from the 75 percent Rock Mod to the 85 percent version will cost you about 8 to 10 fps. Simply put, if you’re trying to squeeze a few fps out of your bow, go with the 75 percent Rock Mod. If you prefer a lighter holding weight at full draw, go with the 85 percent Rock Mod.

When switching the Chill to the 75 percent Rock Mod, I noticed the draw cycle felt a bit stiffer, largely because it is a shorter bow. It didn’t seem to appreciably affect my tune or my point of impact. Keep in mind, this was mostly a speed-test. If I were going to install these Rock Mods permanently, I would have done more fine-tuning.

It would seem that a bow modified to have an 85 percent let-off wouldn’t feel that much different from 80 percent, but it was quite noticeable to me. It felt considerably easier to hold, which was nice, and when it came time to let down it felt like the string needed a little encouragement to go forward. Again, it’s all about personal preference.

My final step was to take advantage of one more feature of the Chill-X. It is available in draw lengths up to 31 inches, so I ordered an additional set of 30.5-inch Rock Mods to hunt with. That’s my true draw length, but I’ve been shooting 30 inches for years because that is what most flagship bows max out at. After all the testing, I fitted the new bow with the 85 percent Rock Mod because I’m primarily setting this bow up for accuracy rather than speed, and I can hold steadier and longer in hunting situations with the higher let-off. With that setup I was shooting the 350-grain arrow at 326 fps and my 446-grain hunting arrow at 292.6 fps. That computes to 85 foot-pounds of kinetic energy, more than enough for just about any game you can imagine. I then set-up my Chill-R as a speed bow with the 75 percent Rock Mods and easily broke the 300 fps mark with my real-life hunting weight arrow.

Now, in the interest of consistency, Bowhunter TV co-host Mike Carney also ran similar tests on his three Chill versions, and at his 28-inch draw length the results were proportionately identical.

Mike’s comments are as follows:

I tested my 70-pound Chill, Chill R and Chill X in a similar manner as Curt, but at a more common draw length of 28 inches, with 392- and 433-grain arrows. Because my true draw is actually 28-1/4 inches, the new Rock Mods felt slightly short compared to the original 80 percent modules with their attendant longer valley, into which you can pull a bit farther. The new Rock Mods, on the other hand, stop dead and hard at their specified length.

For those who have draw lengths outside of whole or half-inch increments, you can easily rectify that by: judiciously twisting/untwisting the cables equally (which, respectively, will slightly increase/decrease bow poundage); add or subtract twists from the string (much smaller impact to overall poundage); tie a longer or shorter loop connection (no effect on bow poundage).

For my style of hunting and what I like in a bow, the new Chill X fits my overall needs better than any other Mathews I’ve ever shot (and I really like the Chill R). When I originally set the X up and fired a few test shots, I thought I had a 60-pound bow. A quick check of the limb verified it was indeed 70 pounds, but after a few more shots I thought surely I had a mislabeled limb. The smoothness of the draw cycle and super-dead shot response was so startling, I had to take it to the scale to reassure myself. And yup, it was 70.2 pounds.

Another interesting feature of the Chill X worth noting is an innovative new axle system that is actually drilled and tapped on the ends, with metal “hat bushings” inserted in both sides of the limb butt axle holes, four bushings total (the inner bushings appear to be somewhat thicker than the outer bushings). A cap head screw, as opposed to the standard e-clip, is used to “snug” the limb tips up on the floating yoke bearings, which now ride against the inner metal bushing and not the inner sides of the limb tips. This keeps the axle/bushing/bearing/cam system tight and snug, and theoretically could lessen eccentric system friction. Due to the floating yoke and standard Quick Change Axle on previous Chill series bows, in the event any cam lean became evident through either wear or simple tolerance fit, you couldn’t yoke tune the system to eliminate pesky lateral tears as it allows no lateral adjustment. This new threaded axle system and bearing approach is the first I’m aware of, and should keep cam lean in check throughout the draw cycle, from the day you pick up a Chill X – to 200,000 shots down the road.

For whatever reason, in hunting situations I seem to find myself stuck at full draw quite regularly, quivering anxiously for animals to make the next mistake. So for me, the Chill X with 85 percent Rock Mods is the clear choice: on the draw board with a scale, its holding weight measured a feathery 10.4 pounds. If I were planning a Coues deer, decoy antelope, open tundra caribou hunt or the like, I would probably go with my Chill R and 75 percent mods due to that outfit’s sheer speed and arrow trajectory advantage, even though it’s a slightly stiffer draw cycle.

Wells’ Summary:
It’s hard to believe, but the new Chill-X has an even smoother, silkier draw cycle than its predecessors, largely due to the longer 35-inch axle-to-axle length. In addition, the AVS DYAD Cam System features an enlarged perimeter weight, helping this longer bow maintain arrow speed. But the solid back wall provided by the Rock Mods, and the option to go with a 75 percent or 85 percent let-off, makes the Chill-X a complete hunting bow you can customize to your preference.

Or, if you already own a Chill or a Chill-R, you can modify the feel of your bow by switching to your choice of Rock Mods, and no bow press is necessary. Be sure to acquire your Rock Mods from a Mathews dealer, because the letter designations and their attendant draw length differ from the original Chill/Chill R.

In other words, if your 30-inch draw Chill R came with a “C” module, you’ll need to order an “A” Rock Mod to match that draw length.

I didn’t think my Chill-R could get much better, but the Chill-X has proven that false. I love a smooth draw cycle, but when it ends in a solid back wall, and still generates exceptional speed, I’m ecstatic.